It is known that health-promoting effects are attributed to glucans from fungi and yeasts. “Shiitake” fungus (Lentinus edodes) has been attributed effects which can be exploited for many medicinal purposes such as immunestimulation, anti-virus, anti-tumour, etc. Studies of lentinan have shown that it stimulates the immune system of the host in a variety of ways, such as activation of T helper cells, increased production of Interleukin 1 and Interleukin 2, increased antibody production in various forms of cancer, and decreasing the cholesterol level in the blood. (Herbs for Health, jan/feb, 1997; K. Jones, “Shiitake: Medicine in a mushroom”, p. 40-50, 54; Anticancer Res, Vol. 17(4A), 1997; H. Matsouka, “Lentinan potentiates immunity and prolongs the survival time of some patients”, p. 2751-2755; Adv Appl Microbiol, Vol. 39, 1993; S. C. Jong, “Medicinal and therapeutic value of the shiitake mushroom”, p. 153-184, Int J Immunopharmacol, Vol. 14, 1992; K. Irinoda, “Stimulation of microbiocidal host defence mechanism against aerosol influenza virus infection by lentinan, p. 971-977., Jpn J Cancer Res, Vol. 76(1), 1985; D. Herlyn, “Monoclonal antibody-dependent murine macrophage-mediated cytotoxicity against human tumors is stimulated by lentinan, p. 37-42).
One active ingredient of Lentinus edodes is termed lentinan, a polysaccharide based compound described as a beta-(1,3) glucan backbone with beta-(1,6) side chains.
“Solid-state” reactors are routinely used for culturing fungi such as Lentinus edodes. This is a technology which is used for many purposes such as composting, production of biological products such as enzymes, soy sauce, acetic acid, and the like.
For the production of lentinan, Lentinus edodes can be cultivated on a suitable solid matrix provided by stems of tree or chips of wood to which is often added chemical compounds supporting the growth of mycelium and development of the fruiting bodies, where most of the lentinan is localised. The fruiting bodies are harvested, either by hand or mechanically, and are subsequently dried and ground to a powder which can be used as it is, or used in tablets, or sent for further processing such as extraction of lentinan.
The methods used for culturing fungi such as Lentinus edodes, harvesting and subsequently drying the fruiting bodies, and optionally extraction of lentinan, are well known for the skilled person. The cultivation time can be from four to ten weeks with few possibilities for controlling the process. This results in a fungal growth, and in turn, in an amount of lentinan produced which is not the same for each batch carried out. Also, extraction of lentinan from the fungal material is time consuming and process intensive.
Kim et al. (2001, Biotechnology Letters, 23, 513-517) describes extracellular polysaccharides produced by Phellinus lintus in submerged culture; Kim et al. (2002: Letters in Applied Microbiology, 34, 56-61) describes mycelial growth and exobiopolymer production by submerged culture of various edible mushrooms. There is no data available to indicate that any of these extracellular polymers are immune stimulating.
It is generally known to grow mycelium of Basidiomycetes in submerged culture and to obtain active ingredients from the growth medium, see e.g. Aouadi et al 1992 (Carbohydr Polym 17:177-184) and Lee et al 1995 (Prog Plant Polym Carbohydr Res, B. Behrs Verlag, Hamburg, Del.) and Hatvani 2001 (Int J Antimicrob Agents 17:71-). However, none of the references discloses the isolation of extracellular components with immune stimulating activities. Furthermore, none of the references disclose that extracellular polysaccharides have different activities from their intracellular counterparts.
It is therefore an object of the present invention to provide novel methods for production of extracellular immune stimulating agents with higher level of activity than the hitherto known intracellular counterparts.